The frequencies and intensities of the Raman spectrum of thermally polymerizing styrene were measured in order to confirm (or correct) the mode assignments in the literature and to observe the effect of polymerization on the Raman active modes. The spectra were measured over a period of three weeks while an originally highly purified sample of monostryrene was kept at about 100 °C. The polymer vibrations are identified with their monomer ’’origins’’ which are in turn compared to known benzene (or benzene derivatives) and ethylene (or vinyl group) vibrations.

The Raman spectrum of thermally polymerizing styrene has been recorded for temperatures of 100 and 70 °C. The intensities of the ν9 (C = C stretch mode) and ν14 (C–H bending mode) in the vinyl group are used as an indicator of the percent conversion from monomer to polymer. These intensities, normalized to that of ν24 (phenyl breathing mode), are compared to the depolarized Rayleigh intensity of polymerizing styrene. It is suggested that there is very little orientational correlation between the polymer and monomer molecules.

Magic‐angle spinning fails to eliminate the effect of dipolar coupling on the spectrum of a spin‐1/2 nucleus (e.g., 13C ) coupled to a quadrupolar nucleus (e.g., 14N). A quantitative theory of this phenomenon, based on an adiabatic approximation, is presented, together with numerical simulations of spectra. The spectrum is sensitive to the sign and magnitude of the electric‐field gradient at the quadrupolar nucleus, the angles between principal axes of the dipolar and quadrupolar interaction tensors, and the orientation of the spinning axis with respect to the external magnetic field.

The Raman reorientational correlation functions and the reorientational correlation times τϑ for the ν1, ν2, and ν5 bands of SF6 have been obtained in the temperature range 253 – 473 °K and at pressures up to 1865 bar. The plot of τϑ(Raman) vs τJ (obtained from the NMRrelaxation times) clearly indicates that the reorientational relaxation of SF6 follows the Fokker–Planck–Langevin (FPL) model in the low density region. The experimental correlation functions were compared with correlation functions computed with the extended diffusion (ED) model and the FPL model. Both models reproduce the experimental correlation functions with the same accuracy; the values of angular momentumcorrelation times τJ used to produce the functions are approximately the same and close to the τJ values obtained from NMR19F spin–lattice relaxation times. However, the fitting procedure, i.e., comparison of experimental correlation functions with the theoretical ones, does not allow an unambiguous conclusion as to which of the models describes the molecular reorientation of SF6. Another important finding of this study is the observation of a nonlinear behavior of the plot of τϑ vs η/T (η is the viscosity) Hynes etal. Detailed analysis of the ν1 band is presented and it is shown that vibrational–rotational coupling is responsible for the ν1 band shape.

An EPR study is performed on Mn2+dopedsingle crystals of lithium ammonium tartrate monohydrate (LAT), both in the paraelectric and ferroelectric phases. The Mn2+EPR spectra in the paraelectric phase are attributed to Mn2+ substituting for NH+4 (1) and associated with a neighboring Li+vacancy. The phase transition at Curie temperature (∼98 K) is found to be of the second order. From the fourfold increase in the number of magnetically distinguishable complexes on going from the paraelectric to the ferroelectric phase and subsequent data for the monodomain crystal, the existence of four kinds of domains is confirmed. The present EPR results on Mn2+ are combined with the previously reported EPR results on Cr3+, and the symmetry of the ferroelectric phase which was believed to be monoclinic (P21) until now is concluded to be triclinic. The triclinic symmetry explains the previously reported but unexplained anomalies in the dielectric constant εaa and elastic compliance SE44 at Tc. The triclinic ferroelectric phase allows for four kinds of domains, viz., I, Ia, Ic, and Ib. The domains Ia and Ic are related to domain I by a twofold rotation about the a and c axes, respectively, and the domains I and Ib are related by a twofold rotation about the b axis. The polarization reversal process involves the necessary destruction of one of the two kinds of domains I and Ib (or Ia and Ic).

Two kinds of ethyl radicals have been observed in Xe matrices depending upon the reactions of radical formation. The CH3 group in C2H5(I) formed from H abstraction by H atoms at temperatures below 50 K exhibits an ESRhyperfine pattern characteristic of tunneling rotation in a threefold hindering potential, whereas that in C2H5(II) formed from homolytic scission of the C–H bond exhibits a conventional spectrum typical of free or random hopping rotation with a small barrier. The g and hyperfine coupling tensors indicate that both the ethyl radicals possess a conventional planar or nearly planar structure. It is concluded that the difference in the internal motion arises from an environmental effect which lowers the rotational symmetry from a six‐ to threefold potential. The tunneling splitting has been determined to be 450 MHz for C2H5(I). From this the barrier to internal rotation is estimated to be about 1 kcal/mol. In estimating the barrier height the influence of the interaction of the CH2 group with the surroundings is taken into consideration. The contribution of a zero‐point torsional amplitude in the averaging process of the β‐proton coupling constant is also discussed.

This paper presents the phase diagram of acetic acid below 0 °C and 2 kbar, and the x‐ray powder diffraction pattern and the far‐infrared absorptionspectrum of acetic acid II at ∼100 °K and atmospheric pressure. The x‐ray powder diffraction pattern of acetic acid I and the far‐infrared absorption spectra of acetic acid I and propanoic acid have been remeasured and are presented for comparison. The transition from acetic acid I to II becomes very slow below −20 °C, so that acetic acid II can not be readily prepared below 1050 bar. The extrapolation of the equilibrium line suggests that phase II is the stable phase at atmospheric pressure below about −60 °C. Acetic acid II does not convert rapidly to acetic acid I at atmospheric pressure below −34 °C. The transition pressure at 0 °C is 1135±18 bar, compared with previous values of 1106 and 1064 bar. The x‐ray powder pattern of phase II has been indexed on the monoclinic cell a = 13.30 Å, b = 10.39 Å, c = 8.59 Å, β = 86.1°, Z = 16. The x‐ray data and the far‐infrared spectra, which can not be fully interpreted, both suggest that phase II, like phase I, contains chains of hydrogen‐bonded monomers which are packed in a slightly different way in the two phases.

The microwave spectra of CH3CH2PH211BH3, CH3CH2PH210BH3, and CH3CH2PH211BD3 have been recorded in the region 18.0–39.0 GHz and those of CH3CH2PD211BH3 and CH3CH2PD211BD3 in the range 26.5–39.0 GHz. a‐type transitions were observed and R‐branch assignments have been made for all isotopes in the ground vibrational state. From the relative intensities of the microwave transitions, the Stark effect, and the experimental rotational constants, it has been determined that the assigned spectra result from the trans conformer which is believed to be more stable than the gauche form at ambient temperature. The dipole moment components for trans‐ethylphosphine–borane were determined from the Stark effect to be ‖μa‖ = 4.66±0.01, ‖μb‖ = 1.34±0.03, and ‖μt‖ = 4.85±0.02 D. With reasonable assumptions for the ethyl moiety, the following structural parameters for trans‐ethylphosphine–borane were calculated: r(B–P) = 1.914±0.018 Å, r(B–H) = 1.205±0.013 Å, r(P–H) = 1.408±0.016 Å, r(P–C) = 1.823±0.016 Å, ∢BPC = 115.0°±1.1°, ∢PBH = 106.1°±3.4°, ∢CPH = 103.4°±3.7°, and ∢PCC = 115.1°±2.5°. These results are compared to similar quantities in some analogous molecules.

Photoionization efficiency (PIE) data for SO2+ have been obtained with a wavelength resolution of 0.14 Å (FWHM) in the region 625–1005 Å using the molecular beam method. The ionization energy (IE) of SO2 was determined to be 12.348±0.002 eV (1004.08±0.20 Å). Similar to the observation in the PIE curve for O3+, the spacing for steplike structure observed near the threshold was found to be irregular. Weak structures which arise by autoionization from different vibrational states of Rydberg levels were also resolved in this region. The analysis gives average vibrational spacing of 386, 428, 716, 745, 911, 938, and 956 cm−1 for these Rydberg states. The appearance energy (AE) for the photodissociative ionization processes SO2+hν→SO++O+e− and S++O2+e− were measured to be 15.953±0.010 eV (777.2±0.5 Å) and 16.228±0.030 eV (764±1.5 Å), respectively. Using the AE for the formation of SO+ from SO2, and the heats of formation of SO2, SO, and O, the IE of SO is deduced to be 10.28±0.02 eV. This value is in excellent agreement with that reported previously by Dyke etal. From the observed IE (11.72±0.03 eV) of (SO2)2, the IE of SO2, and the estimated binding energy (0.03 eV) of (SO2)2, the bond dissociation energy of SO2+ ⋅ SO2 is found to be 0.66±0.04 eV. Using the measured AE (15.38±0.06 eV) for S2O3+ production from (SO2)2, a lower bound for the binding energy of SO+ ⋅ SO2 was calculated to be 0.60 eV.

Electron spin echo modulation studies have been carried out for Nd3+ in methanol glasses at 4.2 K. By using the partially deuterated methanols (CH3OD and CD3OH), analysis of deuterium modulation in three‐pulse electron spin echo decay curves gives the distances and numbers of Nd–D(OD) and Nd–D(CD3) interactions. It is found that Nd3+ is coordinated by nine equivalent methanol molecules, with distances of Nd–H (OH) of 3.1 Å and Nd–H (CH3) of 4.0 Å. These distances establish that the molecular dipole of methanol is oriented toward Nd3+.

The formation of helium and argon glyoxal complexes has been observed. Their lines and bands have been identified from fluorescence excitation spectra in a supersonic jet. Rapid dissociation of the complexes has been shown for all vibronic levels. Further, it has been shown that this dissociation proceeds either to fluorescent or nonfluorescent levels, depending on the vibronic energy and the complex size. The nonfluorescent state has been identified as the phosphorescent 3Au state.

An interpretation of infrared intensities of ethylene and its deuterated derivatives is presented in this paper; different kinds of parameters, namely, molecular dipole derivatives, electro‐optical parameters, polar tensors and effective charges, derived from infrared intensity data are compared. From this comparison and from a further comparison with the quantum mechanical calculations the most likely signs of dipole moment derivatives ∂M/∂Qi seem to be (+ −− ++); this choice of signs leads to a positive equilibrium bond dipole moment μCH0 (C−–H+) and to a decreasing of μCH when the bond is stretched. These results, however, need a further check on other molecules containing the vinyl group before being considered final. In this paper it is also shown that electro‐optical parameters are very useful for interpretative purposes.

The application of deuterium NMR spectroscopy of molecules dissolved in liquid crystalline solvents to study intramolecular dynamic processes is demonstrated using the ring inversion kinetics of cyclohexane‐d12. The spectra of C6D12 dissolved in phase V and in hexyloxyazoxybenzene were studied over the temperature range −36 to +115 °C, and were found to exhibit a very pronounced line shape variation with temperature. At low temperatures (<−10 °C) the spectrum consists of two symmetric doublets due to the axial and equatorial sites. The doublet splittings are due to the quadrupole interactions of the corresponding deuterons. Upon increasing the temperature the lines broaden until finally the spectrum transforms into a single doublet with a spacing corresponding to the mean quadrupole splitting of the axial and equatorial deuterons. In an Appendix the line shape theory for two interacting nuclei of spin I = 1 which undergo mutual exchange is presented, and this theory is used to quantitatively interpret the experimental spectra of cyclohexane‐d12. The kinetic parameters derived from these results are ΔH≠ = 10.3 kcal/mole, ΔS≠ = +0.5 e.u., and 1/τ(at 300 °K) = 1.5×105 sec−1. The results are compared with corresponding data obtained in isotropic solvents.

The Brownian dynamicscomputer simulation method is applied to a dilute system of charged spheres dispersed in a very dilute electrolyte. The parameters of this modelsystem are chosen to match those of an aqueous dispersion of highly charged and strongly interacting polystyrene spheres, on which a number of photoncorrelation spectroscopy studies have recently been made. The structure factor and the electric field autocorrelation functions calculated by the Brownian dynamics method agree with the experimental data provided that allowances are made for the effects of polydispersity and multiple scattering. A few commonly used approximations for analyzing the dynamic properties of many particle systems are also examined.

A Bloch equation describing infrared multiphoton absorption in an isolated polyatomic molecule is derived from first principles. The molecule is divided into a ’’system’’ mode which interacts directly with the laser field and a ’’bath’’ consisting of the remaining modes which interact with each other and the system mode via intramolecular vibrational coupling. In addition to describing the evolution of the system, the derived equation keeps track of changes in the bath state and the resulting changes in the bath–system interaction which occur as the bath gains energy. Unlike the master (or rate) equation for optical pumping, the Bloch equation is valid for arbitrary ratios W/Ω of the intramolecular relaxation rate W/h/ to the Rabi frequency of the system mode Ω/h/. The equation derived differs from certain Bloch equations previously proposed on phenomenological grounds by the appearance of off‐diagonal coupling terms. These terms may significantly reduce the vibrational dephasing rate and thus affect net pumping rates and optical line shapes for vibrationally excited molecules.

We present a theory for intramolecular vibrational relaxation in polyatomic molecules. The theory postulates the existence of a restriction on the magnitudes of matrix elements connecting zero‐order states which favors coupling between vibrational modes. Specifically, the matrix elements are assumed to depend on two parameters, one determining the overall magnitude of coupling, and the other the rate of falloff with increasing quantum exchange. We use this ’’restricted quantum exchange’’ (RQE) hypothesis to derive analytic expressions for T1 (energy‐transfer) and T2 (coherence‐loss) relaxation rates which depend only on the two coupling parameters, the average molecular frequency, the number of modes, the energy in the molecule, and (for T1) the size of the energy transfer. In the derivation we obtain analytic expressions for the number of pairs of states on an energy shell related to each other by exchange of a fixed number of quantua M. The analysis has been carried out for arbitrary M, allowing us formally to include the effects of all higher order couplings and to show rigorously when they can be eliminated. The resulting T1 and T2 relaxation rates and associated linewidths exhibit saturation with increasing vibrational energy, a property which has been shown to be essential to obtaining reasonable cross sections for multiphoton excitation. We propose on the basis of restricted quantum exchange a simple explanation for the observed narrowing of the linewidths of benzene with increasing vibrational quantum number.

A method is developed for assessing the accuracy of scattering observables calculated within the framework of the infinite order sudden (IOS) approximation. In particular, we focus on the energy sudden assumption of the IOS method and our approach involves the determination of the sensitivity of the IOS scattering matrix SIOS with respect to a parameter which reintroduces the internal energy operator ?0 into the IOS Hamiltonian. This procedure is an example of sensitivity analysis of missing model components (?0 in this case) in the reference Hamiltonian. In contrast to simple first‐order perturbation theory a finite result is obtained for the effect of ?0 on SIOS. As an illustration, our method of analysis is applied to integral state‐to‐state cross sections for the scattering of an atom and rigid rotor. Results are generated within the He+H2 system and a comparison is made between IOS and coupled states cross sections and the corresponding IOS sensitivities. It is found that the sensitivity coefficients are very useful indicators of the accuracy of the IOS results. Finally, further developments and applications are discussed.

Reactions of N2+ion beams with the surface of clean polycrystallinealuminum over the energy range of 300–4000 eV are studied by the techniques of x‐ray and UVphotoelectron spectroscopy (XPS and UPS) and Auger electron spectroscopy(AES). The reaction produces a nitride layer which the depth–concentration profiles reveal to be a superposition of two distributions: the first is a continuous AlN phase at the near surface to a depth of ∼20 Å and the second is a region of lower nitrogen concentration tailing deeper into the Al substrate where a complete AlN phase has not been established. The AlN film is characterized by the agreement of the binding energies of the N 1s (397.3 eV) and Al 2p (74.1 eV) lines, of the kinetic energy of the AlKLL line (1338.9 eV), and of the Auger parameter (1463.0 eV) with a known standard of AlN. The N/Al ratio initially increases linearly with the nitrogen ion dose at low concentrations and finally reaches a steady state condition, determined by the opposing rates of nitridation and sputtering by impinging ions, at a dose of ∼1×1016 ions cm−2. The reaction cross section is found to vary from 2.0×10−16 to 4.7×10−17 cm2 over the ion energy range of 0.3–1.0 keV. A reaction mechanism which is supported by these results is discussed.

Chemiluminescence has been observed in the single collision reaction of boron atoms with O2, SO2, N2O, NO2, and H2O2. The experiments were performed in a beam‐gas apparatus using photon counting to detect the optical signals. The electronically excited A2π state of BO was observed in all the reactions. In addition, the BO2(A2πu) state was observed in the reaction of boron with SO2. Cross sections for the production of electronically excited molecules were determined. These cross sections for the reactions with O2, SO2, N2O, NO2, and H2O2 are, respectively, 0.048, 0.0078, 0.01, 0.023, and 0.005 Å2. In the reactions of boron with SO2 the branching ratio was obtained for the two observed chemiluminescent reaction channels. The vibrational distributions in the electronically excited state of BO were determined in the reactions where the spectra were adequately resolved. Some implications of the results are discussed.

Direct excitation of overtone vibrations combined with time‐resolved detection of product chemiluminescence produces both overtone vibration excitation spectra and directly measured unimolecular decay rates of tetramethyldioxetane. The spectra show increasingly pure local mode character in higher vibrational levels and exhibit splittings which arise from nonequivalent sites occupied by methyl hydrogens. The temporal evolution of the signal reflects the unimolecular decomposition rate of the highly vibrationally excited molecule, and comparing the observed behavior to Rice–Ramsperger–Kassel–Marcus theory calculations shows that they adequately describe the decomposition if properly averaged over the thermal vibrational energy content of the molecule.